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ANDROID: vfs: add d_canonical_path for stacked filesystem support

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Inotify does not currently know when a filesystem is acting as a wrapper
around another fs. This means that inotify watchers will miss any
modifications to the base file, as well as any made in a separate stacked
fs that points to the same file.
d_canonical_path solves this problem by allowing the fs to map a dentry to
a path in the lower fs. Inotify can use it to find the appropriate place to
watch to be informed of all changes to a file.

Test: Pixel 4.19
Bug: 171780975
Change-Id: I09563baffad1711a045e45c1bd0bd8713c2cc0b6
Signed-off-by: Daniel Rosenberg <drosen@google.com>
[astrachan: Folded 34df4102216e ("ANDROID: fsnotify: Notify lower fs of
            open") into this patch]
Signed-off-by: Alistair Strachan <astrachan@google.com>
Signed-off-by: Yongqin Liu <yongqin.liu@linaro.org>
Signed-off-by: Alessio Balsini <balsini@google.com>
This commit is contained in:
Alessio Balsini 2020-10-27 13:24:03 +00:00
parent c0be21f504
commit 54b41388f5
3 changed files with 25 additions and 3 deletions
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16
fs/notify/inotify/inotify_user.c
View file

@ -702,6 +702,8 @@ SYSCALL_DEFINE3(inotify_add_watch, int, fd, const char __user *, pathname,
struct fsnotify_group *group;
struct inode *inode;
struct path path;
struct path alteredpath;
struct path *canonical_path = &path;
struct fd f;
int ret;
unsigned flags = 0;
@ -747,13 +749,23 @@ SYSCALL_DEFINE3(inotify_add_watch, int, fd, const char __user *, pathname,
if (ret)
goto fput_and_out;
/* support stacked filesystems */
if (path.dentry && path.dentry->d_op) {
if (path.dentry->d_op->d_canonical_path) {
path.dentry->d_op->d_canonical_path(&path,
&alteredpath);
canonical_path = &alteredpath;
path_put(&path);
}
}
/* inode held in place by reference to path; group by fget on fd */
inode = path.dentry->d_inode;
inode = canonical_path->dentry->d_inode;
group = f.file->private_data;
/* create/update an inode mark */
ret = inotify_update_watch(group, inode, mask);
path_put(&path);
path_put(canonical_path);
fput_and_out:
fdput(f);
return ret;

3
include/linux/dcache.h
View file

@ -151,7 +151,8 @@ struct dentry_operations {
int (*d_manage)(const struct path *, bool);
struct dentry *(*d_real)(struct dentry *, const struct inode *);
ANDROID_KABI_RESERVE(1);
ANDROID_KABI_USE(1, void (*d_canonical_path)(const struct path *,
struct path *));
ANDROID_KABI_RESERVE(2);
ANDROID_KABI_RESERVE(3);
ANDROID_KABI_RESERVE(4);

9
include/linux/fsnotify.h
View file

@ -211,11 +211,20 @@ static inline void fsnotify_open(struct file *file)
{
const struct path *path = &file->f_path;
struct inode *inode = file_inode(file);
struct path lower_path;
__u32 mask = FS_OPEN;
if (S_ISDIR(inode->i_mode))
mask |= FS_ISDIR;
if (path->dentry->d_op && path->dentry->d_op->d_canonical_path) {
path->dentry->d_op->d_canonical_path(path, &lower_path);
fsnotify_parent(&lower_path, NULL, mask);
fsnotify(lower_path.dentry->d_inode, mask, &lower_path,
FSNOTIFY_EVENT_PATH, NULL, 0);
path_put(&lower_path);
}
fsnotify_parent(path, NULL, mask);
fsnotify(inode, mask, path, FSNOTIFY_EVENT_PATH, NULL, 0);
}